KR100866175B1 - Glass substrate for information recording medium and information recording medium employing same - Google Patents

Abstract

In the glass for chemically strengthened information recording medium, the reinforcement layer 13 by chemical strengthening is present on the outer circumferential surface and the inner circumferential surface, and is not substantially present on the upper surface 11 and the lower surface 12 on which the information recording layer is formed. Do not Thereby, shape precision, such as flatness, and intensity | strength can be improved, without requiring a highly accurate substrate grinding | polishing technique.

Polishing, fracture toughness

Description

Glass substrate for information recording medium and information recording medium using the same {GLASS SUBSTRATE FOR INFORMATION RECORDING MEDIUM AND INFORMATION RECORDING MEDIUM EMPLOYING SAME}

The present invention relates to a glass substrate for an information recording medium (hereinafter referred to simply as a "glass substrate"), and more particularly to a glass substrate used as a substrate for an information recording medium such as a magnetic disk, magneto-optical disk, DVD, or MD. It is about.

Conventionally, as a substrate for a magnetic disk, an aluminum alloy is generally used for a stationary type such as a desktop computer or a server, while a glass substrate is generally used for a portable type such as a notebook type computer or a mobile computer, but the aluminum alloy is easily deformed and its rigidity is insufficient. This does not provide sufficient smoothness of the substrate surface after polishing. In addition, when the head mechanically contacts the magnetic disk, there is a problem that the magnetic film is easily peeled from the substrate. For these reasons, there are few variations, It is anticipated that glass substrates with good smoothness and high mechanical strength will be widely used in portable as well as stationary devices and other home information devices in the future.

BACKGROUND ART As a glass substrate, chemically strengthened glass is known in which compressive strain is generated by substituting an alkali element on the surface of a substrate with another alkali element to improve mechanical strength. In the production of chemically strengthened glass, chemically strengthening treatment has generally been carried out after the polishing treatment, and the chemically strengthened glass substrate has been released as a product without being reworked as it is. As a result of the chemical treatment, it was necessary to perform a polishing treatment to achieve higher flatness than would eventually be required to allow for the inevitable degradation of the flatness of the glass substrate. Moreover, when deformation | transformation arises in a glass substrate by chemical processing, it is forced to discard them as a defective product. This makes it difficult to achieve a sufficiently high yield. In order to overcome this inconvenience, for example, Patent Document 1 proposes a technique for improving the productivity and related results by polishing the glass substrate after chemical strengthening treatment.

Patent Document 1: Japanese Unexamined Patent Publication No. 2000-76652 (published March 14, 2000)

Disclosure of the Invention

Challenges the invention seeks to solve

In the proposed technique, the reinforcing layer on the main surface is removed by polishing after the chemical reinforcing treatment, but the reinforcing layer having a predetermined thickness is left after the polishing treatment. For this reason, if the reinforcement layer after a grinding | polishing process is nonuniform, deterioration of shape quality, such as flatness, will arise. To prevent this, the upper and lower surfaces of the glass substrate must be homogeneously polished, and a high precision polishing technique is required.

 An object of the present invention is to provide a glass substrate for an information recording medium that is excellent in shape accuracy such as flatness and has high strength without requiring a high-precision polishing technique.

Another object of the present invention is to provide a glass substrate for an information recording medium which is excellent in mechanical strength and durability and capable of high density recording.

Means to solve the problem

According to the present invention, a glass substrate for a chemically strengthened information recording medium, wherein a reinforcing layer formed by chemical strengthening exists on the outer circumferential surface and the inner circumferential surface, but substantially on the surface on which the information recording layer is formed (hereinafter referred to as "recording surface"). There is provided a glass substrate for an information recording medium which does not exist. In addition, in this specification, chemical strengthening means generating compressive stress on the glass substrate surface by substituting the ion near the glass surface with the ion which has a larger ion radius in the temperature range below the glass transition point of a glass substrate.

Here, from the viewpoint of stably forming a reinforcement layer of a suitable thickness by chemical strengthening treatment, and from the viewpoint of further improving mechanical strength, chemical durability, and the like, the glass substrate according to the present invention contains the following glass component on its recording surface. Preference is given to:% by weight SiO ₂ : 40-75%, Al ₂ 0 ₃ : 3-20%, B ₂ 0 ₃ : 0-8% (including 0), R ₂ 0 (R = Total amount of Li, Na, K): 5-15%, SiO ₂ + Al ₂ 0 ₃ + B ₂ 0 ₃ : 60-90%, of R'0 (R '= Mg, Ca, Sr, Ba, Zn) Total amount: 0-20% (including 0), TiO ₂ + ZrO ₂ + Ln _x 0 _y : 0-15% (including 0, and Ln _x O _y is a lanthanoid metal oxide and Y Means at least one compound selected from the group consisting of ₂ O ₃ , Nb ₂ 0 ₅ , and Ta ₂ O ₅ ),

It is preferable to satisfy 1.5 <Al ₂ 0 ₃ / B ₂ 0 ₃ or B ₂ 0 ₃ = 0%. Here, "%" means "% by weight" unless otherwise specified.

Here, in order to reduce the alkali elution amount, the lower limit of K ₂ O content is preferably 0.5% by weight%. Moreover, for a more stable structure of the glass and its improved rigidity, the total amount of TiO ₂ + ZrO ₂ + Ln _x O _y is preferably in the range of 0.5% -13% by weight.
Inelastic modulus (E / ρ) is 30 or more, Vickers hardness Hv is 450-650, alkali elution A is 350ppb or less per 2.5 inch disc, Si elution S is 500ppb or less per 2.5 inch disc, fracture toughness Kc is O.80MPa It is preferable to have more than / m ^1/2 .

In addition, fracture toughness value Kc was computed from the following formula using the Vickers hardness tester based on the indentation made with Vickers indenter on condition of 500g of load and 15 second of load time (refer FIG. 3).

Kc = 0.018 (E / Hv) 1/2 (P / C 3/2) = 0.026 E 1/2 P 1/2 a / C 3/2

(Kc: fracture toughness (Pam ^1/2 ), E: modulus of elasticity (Pa), Hv: Vickers hardness (Pa), P: pressing load (N), C: half of the mean of crack length (m ), a: Half (m) of the average of the diagonal lengths of the indentation.Si elution amount S and alkali elution amount A are 50 ml of reverse osmosis membrane water at 80 ° C. for a 2.5 inch disk substrate prepared by polishing a recording surface of a glass substrate subjected to reinforcement. After immersion for 24 hours at, the eluate is analyzed by ICP emission spectrometry and the alkali elution is the total amount of Li, Na and K. The inelasticity (E / ρ) is the Young's modulus E divided by the specific gravity p. The Young's modulus E was measured according to the dynamic modulus test method of the elastic test method of the Japanese industrial Standards (JIS) R 1602 fine ceramics, and the specific gravity p was measured in distilled water at 25 ° C. by the Archimedes method. The hardness Hv was measured using a Vickers hardness tester under a load of 100 g and a load time of 15 seconds. Measure

And according to this invention, the information recording medium provided with the information recording layer in the said glass substrate is provided.

Effects of the Invention

Since the glass substrate for an information recording medium of the present invention has a reinforcing layer on the outer circumferential surface and the inner circumferential surface, breakage or damage starting from the outer and inner circumferential surfaces hardly occurs, and the effective strength can be improved. In addition, the impact resistance is excellent, and thus, the glass substrate is greatly damaged during handling in the manufacturing process and the like, and even if broken, it is less likely to scatter greatly and contaminate the process. Since the reinforcing layer is substantially absent on the surface where the information recording layer is formed, the surface flatness and smoothness are high. This enables high density recording when formed into an information recording medium.

And in the information recording medium of this invention, since the information recording layer was formed in the glass substrate, the damage in a manufacturing process can be reduced and the yield rate of a product can be improved. In addition, improved durability can increase the reliability of the picture and the recording medium.

Implement the invention  Best form for

MEANS TO SOLVE THE PROBLEM The present inventor paid much attention to the fact that the breakage | damage and the breakage of a glass substrate generate | occur | produce a starting point from an internal and an external cross-section, and since earnestly examined, the chemical reinforcement was carried out not on the upper and lower surfaces of the glass substrate which is a recording surface, but on the inner and outer peripheral surfaces of a glass substrate. By forming the reinforcement layer by using the present invention, it has been found that it is possible to effectively prevent breakage or damage of the glass substrate and to minimize degradation in shape accuracy such as flatness of the glass substrate which is likely to occur due to chemical strengthening. This finding led the inventor to conceive the present invention.

Specifically, a reinforcing layer is formed on the inner circumferential surface and the outer circumferential surface of the glass substrate, which are the starting points of breakage and damage. This helps to increase the strength of the glass substrate. The absence of the reinforcing layer on the recording surface suppresses the shape change of the glass substrate due to the stress of the reinforcing layer.

In this invention, chemical strengthening is achieved by immersing a glass substrate in the nitrate solution heated below glass transition point. This causes ions near the glass surface to be replaced with ions having a larger ionic radius, and generates compressive stress on the glass substrate surface to achieve strengthening. As the chemical strengthening solution, one or more mixed with a molten salt such as potassium nitrate, sodium nitrate, potassium carbonate, a molten salt of a mixture of one or more such salts, or a salt containing ions such as Cu, Ag, Rb, Cs, etc. There are molten salts of these salts.

The thickness of the reinforcing layer by the chemical treatment is adjusted by the heating temperature of the chemical reinforcing solution and the immersion time of the glass substrate, as understood from the examples described later (see Table 2). The higher the solution temperature and the longer the immersion time, the thicker the reinforcement layer is. For the balance between maximizing the strength of the glass substrate and shortening the polishing treatment time, the thickness of the reinforcing layer is preferably in the range of 3-20 μm. The heating temperature of the chemical strengthening solution is appropriately determined in consideration of the glass transition point of the glass substrate, usually in the range of 280-660 ° C, more preferably in the range of 320-500 ° C. The immersion time is preferably in the range of 0.1 hour to several ten hours.

A method of removing the reinforcing layer by polishing the upper and lower surfaces after immersing the glass substrate in a chemical reinforcing solution so that the reinforcing layer by chemical reinforcement exists on the inner and outer circumferential surfaces of the glass substrate, not on the upper and lower surfaces of the glass substrate, which is the recording surface. Although a method of coating the upper and lower surfaces of the glass substrate with a masking member and immersing it in a chemically strengthening solution while exposing only the inner and outer peripheral surfaces of the glass substrate is conceivable, removal by polishing is recommended in consideration of productivity. Hereinafter, the removal method of the upper and lower reinforcement layers by a polishing process is demonstrated.

1 shows a manufacturing process diagram of a glass substrate. The glass block was sliced into a disk having a predetermined thickness, and the glass substrate 1 was cut using a cutter so as to have a concentric inner and outer circumference (Fig. 1 (a)). It is preferable to chamfer or round the inner and outer peripheral ends of the glass substrate 1 here. In the glass substrate 1 of FIG. 1, a chamfer is added. The information recording layer 2 (shown in FIG. 2) is finally formed on the upper and lower surfaces 11 and 12 of the glass substrate 1. And the glass substrate 1 is immersed in the nitrate solution heated to predetermined temperature for predetermined time, and the reinforcement layer 13 is formed below the surface of the glass substrate 1 (FIG. 1 (b)). And the upper surface 11 and the lower surface 12 of the glass substrate 1 are polished deeper than the thickness of the reinforcement layer 13, and the reinforcement layer formed in the upper and lower surfaces 11 and 12 of the glass substrate 1 is carried out. (13) is polished and erased (Fig. 1 (c)). The polishing amount is preferably about 2-10 times the thickness of the reinforcing layer. There is no restriction | limiting in particular as a grinding | polishing method, A conventionally well-known method can be used, For example, brush grinding | polishing, grinding | polishing by an abrasive member, etc. are mentioned. Examples of the abrasive member include cerium oxide, alumina, chromium oxide, zirconium oxide, titanium oxide and the like.

There is no limitation in particular as a component of the glass substrate of this invention. For the stable formation of a reinforcement layer of suitable thickness, and for much higher mechanical strength and chemical durability, the glass substrate according to the invention preferably contains the following glass component by weight in the recording surface: SiO ₂ : 40 -75%, Al ₂ 0 ₃ : 3-20%, B ₂ 0 ₃ : 0-8% (including 0), total amount of R ₂ O compounds (R = Li, Na, K): 5- 15%, SiO ₂ + Al ₂ O ₃ + B ₂ 0 ₃ : 60-90%, total amount of R'O compounds (R '= Mg, Ca, Sr, Ba, Zn): 0-20% (where 0 TiO ₂ + ZrO ₂ + Ln _x 0 _y : 0-15% (Ln _x O _y is selected from the group consisting of lanthanoid metal oxide and Y ₂ O ₃ , Nb ₂ 0 ₅ , Ta ₂ 0 ₅ 1 or more compounds),

1.5 <Al ₂ 0 ₃ / B ₂ 0 ₃ , or B ₂ 0 ₃ = 0%. The limited reason for such a glass component is demonstrated.

First, SiO ₂ is a component that forms a matrix of glass. If the content is less than 40%, the structure of the glass becomes unstable, the chemical durability is lowered, and at the same time, the viscosity property at the time of melting worsens, which impairs the formability. On the other hand, when content exceeds 75%, meltability will worsen, productivity will fall, and sufficient rigidity will not be obtained. Therefore, the content is preferably in the range of 40-75%. More preferred range is 50-72%.

Al ₂ O ₃ enters the matrix of glass and acts to stabilize the glass structure and improve chemical durability. If the content is less than 3%, a sufficient stabilization effect is not obtained, and ion exchange does not proceed stably in the strengthening treatment. On the other hand, when it exceeds 20%, meltability will worsen, and productivity will be impaired. Therefore, the content is preferably in the range of 3-20%. More preferred range is 5-18% of range.

B ₂ O ₃ improves meltability and improves productivity while simultaneously entering the glass matrix to stabilize the glass structure and improve chemical durability. When the content is more than 8%, the viscosity property at the time of melting becomes poor, causing moldability, and at the same time increasing the volatility of the glass solution, resulting in a significant decrease in productivity and stability. Therefore, the content is preferably 8% or less (including 0). The upper limit of more preferable content is 6%.

If the total amount of these three glass components (SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ ), which are skeletal components of the glass, is less than 60%, the glass has a fragile structure. On the other hand, when those total amounts exceed 90%, meltability will fall and productivity will fall. Therefore, the total amount of such glass components is preferably in the range of 60-90%. More preferred range is 68-88%.

Alkali metal oxide R ₂ O (R = Li, Na, K) improves meltability and improves productivity. If the total amount of the alkali metal oxide is less than 5%, the glass substrate can not be sufficiently strengthened by the ion exchange treatment while at the same time not exhibiting sufficient effects on the melt improving properties. On the other hand, when the total amount exceeds 15%, the amount of alkali dispersed between the glass skeletons becomes excessive, the amount of alkali elution increases, and the chemical durability significantly decreases. In addition, the ion exchange reaction proceeds excessively with respect to the reinforcement treatment, making it difficult to control the thickness of the reinforcement layer. Therefore, the total amount of alkali metal oxide is preferably in the range of 5-15%. More preferred range is 7-16% of range. Moreover, in order to acquire the so-called alkali mixing effect which reduces alkali elution amount, it is preferable to make the minimum content of each alkali metal oxide into 0.5%.

The divalent metal oxide R'O (R '= Mg, Ca, Sr, Ba, Zn) not only improves rigidity but also improves meltability and stabilizes the glass structure. When the total amount of R'O exceeds 20%, the glass structure becomes unstable, so that the melt productivity decreases and the chemical durability decreases. Therefore, the content of R'O is preferably 20% or less. The more preferable upper limit of the total amount of R'O is 18%. The suitable content of each component of R'O is as follows.

MgO improves stiffness while improving stiffness. When the content is more than 20%, the glass structure becomes unstable, the melt productivity is lowered and the chemical durability is lowered. Therefore, the content is preferably in the range of 0-19%. More preferred upper limit is 18%.

In addition, CaO improves the coefficient of thermal expansion and stiffness and improves meltability. When the content exceeds 10%, the glass structure becomes unstable, resulting in low melt productivity and low chemical durability. Therefore, the content is preferably in the range of 0-10%. More preferred upper limit is 9%.

SrO improves the coefficient of thermal expansion to stabilize the glass structure and at the same time improve the meltability. If the content exceeds 8%, the glass structure may become unstable. Therefore, the content is preferably in the range of 0-8%. More preferred upper limit is 6%.

BaO exerts the same effect as SrO. If the content exceeds 8%, the glass structure may become unstable. Therefore, the content is preferably in the range of 0-8%. More preferred upper limit is 6%.

ZnO improves chemical durability and stiffness and improves meltability. When the content exceeds 6%, the glass structure becomes unstable, the melt productivity decreases and the chemical durability decreases. Therefore, the content is preferably in the range of 0-6%. More preferred upper limit is 5%.

TiO ₂ strengthens the structure of the glass, improves rigidity and improves meltability. In addition, ZrO ₂ also strengthens the glass structure to improve rigidity and chemical durability. And Ln _x O _y strengthens the structure of the glass and improves the rigidity and toughness. Here, Ln _x O _y means at least one compound selected from the group consisting of lanthanoid metal oxide and Y ₂ O ₃ , Nb ₂ 0 ₅ , Ta ₂ 0 ₅ . Examples of the lanthanoid metal oxide include other kinds of compositions Ln ₂ O ₃ , LnO, and the like, and as Ln, La, Ce, Er, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb , Lu, and the like. If TiO ₂ + ZrO ₂ + Ln _x 0 _y exceeds 15%, the glass becomes unstable, the toughness is greatly reduced, and the devitrification tendency is increased, which leads to a significant decrease in productivity. Therefore, such total amount is preferably 15% or less. More preferred total amount is in the range of 0.5-13%.

In addition, in case the glass composition of the present invention, the content of B ₂ O ₃ is not 0, it is necessary to increase the _{Al 2 0 3 / B 2 0} 3 than 1.5. When Al ₂ O ₃ / B ₂ O ₃ is 1.5 or less, the structure of the glass becomes brittle, and sufficient toughness cannot be obtained. Moreover, in the strengthening treatment, ion exchange does not proceed stably.

A refining agent (clarifier), such as Sb ₂ 0 ₃ as the glass component of the invention may be added in a fine range of 2% or less. As needed, you may add a conventionally well-known glass component and an additive in the range which does not impair the effect of this invention.

There is no restriction | limiting in particular as a method of manufacturing a glass substrate from the said glass component, A well-known manufacturing method can be used so far. For example, the oxides, carbonates, nitrates, hydroxides, and the like corresponding to the raw materials of the respective components are weighed at a desired ratio, and sufficiently mixed into powder to obtain a combination of the raw materials. This is put into, for example, a platinum crucible in an electric furnace heated to 1300-1550 ° C., dissolved and clarified, stirred and homogenized, and then the molten glass is poured into a preheated mold and gradually cooled to form a glass block. . Next, it is reheated to near the glass transition point, and after that, it is gradually cooled and straightened. And the obtained glass block is sliced in disk shape, and it cuts using a core drill so that it may have concentric inner and outer periphery. Or the molten glass is press-molded and formed into disk shape.

It is preferable that the glass substrate which concerns on this invention satisfy | fills the following various physical properties. First, it is preferable that the inelastic modulus (E / ρ) is 30 or more. In glass substrates not subjected to the strengthening treatment, the mechanical strength depends on the rigidity of the substrate. Therefore, when the inelasticity is less than 30, the mechanical strength of the substrate is insufficient, and when the hard disk drive is impacted from the outside when the hard disk drive is mounted, it is easily broken from the fastening portion with the hard disk drive member. More preferred inelastic modulus (E / ρ) is at least 31.

Vickers hardness Hv is preferably in the range of 450-650. If the Vickers hardness is less than 450, damage due to impact or damage in the manufacturing process is likely to occur. On the other hand, if the Vickers hardness Hv is larger than 650, the rate at which the glass substrate can be polished in polishing decreases, making it difficult to obtain a desired smooth surface, and the surface shape of the substrate is adjusted by polishing the tape texture after polishing. Or surface defect correction by tape or scrub cleaning treatment becomes difficult. In order to make Vickers hardness into such a range, the component ratio may be adjusted so that the ion filling rate in glass may be improved, for example in the range which does not reduce the target main physical property. The lower limit with preferable Vickers hardness Hv is 500, and a more preferable upper limit is 630.

The alkali elution amount A is preferably 350 ppb or less per 2.5 inch disk. If the alkali elution amount A is greater than 350 ppb, when a glass substrate is used as the information recording medium, recording films such as magnetic films formed on the surface of the glass substrate are lowered by elution of the alkali component from the substrate. More preferable alkali elution amount A is 320 ppb or less.

Si elution amount S is preferably 500 ppb or less per 2.5 inch disk. Since SiO ₂ is a main component of the glass skeleton, the Si elution amount S becomes an index of water resistance of the glass substrate, that is, stability to water. When the Si elution amount S is more than 500 ppb, water resistance is inferior, production stability in a grinding | polishing or washing | cleaning process in a manufacturing process falls, and storage stability worsens because a glass substrate is easy to be influenced by the moisture in air | atmosphere. The more preferable range of Si elution amount S is 400 ppb or less per 2.5 inch disk.

The fracture toughness Kc is preferably at least 80. When the glass substrate is used as an information recording medium, if the fracture toughness value Kc is less than 0.80, the glass substrate may be cracked due to the pressure applied in the step of forming a recording film such as a magnetic film on the surface of the glass substrate. Moreover, when fracture toughness value Kc is less than 0.80, a board | substrate will be easy to be damaged with respect to the machining of a board | substrate, and a process yield will fall large. The more preferable range of fracture toughness Kc is O.85 or more.

The glass substrates of the present invention can be used to produce discs of 3.5, 2.5, 1.8 inches, or less diameter, the thickness of which is 2 mm or lmm, 0.63 mm, and thinner discs, without being limited in size.

Next, an information recording medium using the glass substrate of the present invention will be described. When the glass substrate of the present invention is used as the substrate of the information recording medium, durability and high recording density are realized. With reference to the drawings, such an information recording medium will be described.

2 is a perspective view of a magnetic disk. This magnetic disk D forms the magnetic film 2 directly on the surface of the circular glass substrate 1. As the formation method of the magnetic film 2, a conventionally well-known method can be used. For example, the method of spin-coating and forming the thermosetting resin which disperse | distributed magnetic particle on a board | substrate, or the method of forming by sputtering and electroless plating is mentioned. The spin-coating method provides a film thickness of about O.3-1.2 μm, sputtering provides a film thickness of about O.04-0.08 μm, and electroless plating is about O.05-0.1 μm. Provide thickness. In view of thinning and high density, film formation due to sputtering and electroless plating is preferable.

The magnetic material used for the magnetic film is not particularly limited, and conventionally known ones can be used, but Ni and Cr are included for the purpose of adjusting the residual magnetic flux density by containing Co exhibiting high crystal anisotropy as its main component in order to obtain high coercive force. Co-based alloys having added thereto are very suitable. Specifically, examples of the alloy containing Co as a main component include CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, CoCrPtSiO and the like. The magnetic film may be divided into a nonmagnetic film (for example, Cr, CrMo, CrV, etc.) to have a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa, etc.) to reduce noise. Instead of the above magnetic materials, granular type magnetic materials having magnetic particles such as Fe, Co, FeCo, CoNiPt, etc. dispersed in a ferrite-based, iron / rare earth-based, nonmagnetic film such as SiO ₂ , BN, etc. It is also possible to use. In addition, the magnetic film may be of any recording type, either internal or vertical.

In addition, in order to improve the slipping of the magnetic head, a thin lubricant may be coated on the surface of the magnetic film. Examples of the lubricant include perfluoropolyether (PFPE), which is a liquid lubricant diluted with a freon-based (CFC-based) solvent.

If necessary, an additional base layer or a protective layer may be formed. The material of the base layer in the magnetic disk is selected according to the magnetic film. As a material of a base layer, at least 1 type or more materials chosen from nonmagnetic metals, such as Cr, Mo, Ta, Ti, W, V, B, Al, Ni, are mentioned, for example. In the case of a magnetic film containing Co as a main component, it is preferable that it is Cr or a Cr alloy from the viewpoint of improving magnetic properties. The base layer may be formed of a single layer or may be a multilayer structure in which the same or different layers are laminated. For example, it may be a multilayer base layer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, NiAl / CrV.

As a protective layer which prevents abrasion and corrosion of a magnetic film, a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenation carbon layer, a zirconium oxide layer, a silica layer, etc. are mentioned, for example. Such a protective layer may be formed in a continuous step with a base layer, a magnetic film, or the like using an in-line sputtering apparatus. The protective layer may consist of a single layer or may consist of a plurality of layers of the same or different types placed on top of each other to form a multilayer protective layer. In addition, it is also possible to form another protective layer on the above-described protective layer or instead of the protective layer. For example, instead of the protective layer, colloidal silica fine particles dispersed in tetraalkoxysilane diluted with an alcohol solvent on a Cr layer may be applied and then fired to form a silicon oxide (SiO ₂ ) layer.

As mentioned above, although the magnetic disk was demonstrated as an example of an information recording medium, the information recording medium is not limited to this, The glass substrate of this invention can also be used for an optical magnetic disk, an optical disk, etc.

1 is a manufacturing process diagram of a glass substrate of the present invention.

2 is a perspective view showing an example of an information recording medium of the present invention.

It is a schematic diagram of the indentation and crack which generate | occur | produce when pressure is applied to the surface of a glass substrate with a Vickers indenter.

4 is a schematic explanatory diagram of an annular bending strength test.

Explanation of the sign

1 glass substrate

2 magnetic film

D magnetic disk

11 Top View (Recording Surface)

12 Bottom (recording side)

13 reinforcement layer

Example  One

Example 1-9, Comparative Example 1-4

For each of the other glass compositions corresponding to each of Examples 1-9 and Comparative Examples 1-4, a predetermined amount of raw powder was weighed into a platinum crucible, mixed, and then dissolved at 1550 ° C. in an electric furnace. After fully dissolving the raw materials, the stirring blade was inserted into the glass melt and stirred for about 1 hour. Then, the stirring blade was taken out and left still for 30 minutes, and the glass block was obtained by pouring a melt into a mold. After that, the glass block is reheated to the vicinity of the glass transition point of each glass, and gradually cooled to did. The obtained glass block was sliced into a disk of thickness 635 mm, and cut using a cutter to have a concentric inner circumference (inner diameter of 20 mm) and outer circumference (outer diameter of 65 mm).

The produced glass substrate was immersed in a nitrate mixed solution of 70 mol% NaNO ₃ and 30 mol% KNO ₃ heated at 350 ° C. for 0.5 hour to form a reinforcing layer below the surface of the glass substrate. The upper and lower surfaces of the glass substrate were roughly polished and fine-polished with cerium oxide to remove a total depth of 100 µm, and then washed to prepare glass substrates of Examples 1-9 and Comparative Examples 1-3. In addition, the grinding | polishing amount in the glass substrate of the comparative example 4 was made into 20 micrometers in total from both upper and lower sides. Various physical properties were evaluated about the produced glass substrate according to the said measuring method and the following measuring method. The measurement results are shown in Table 1.

(Thickness of the reinforced layer)

The outer circumferential surface, the inner circumferential surface, and the recording surface of the glass substrate after the polishing treatment were observed with a polarizing microscope, and the thickness of the reinforcing layer was measured.

(Annular strength ratio)

The annular bending strength test of the glass substrate was done using the apparatus shown in FIG. Specifically, a load was added to the glass substrate as a steel ball, and the load when the glass substrate broke was measured as the breaking load. This toroidal flexural strength test is performed for each case of chemical strengthening and without chemical strengthening, and the ratio of the strength (breakdown load) F when the chemical strengthening to the strength without chemical strengthening is performed. In other words, F _{chemical strengthening} / F _{non-chemical strengthening} was calculated.

(flatness)

The flatness of the glass substrate was measured using a disk shape meter WYK0 400G manufactured by Veeco Instruments.

TABLE 1

Table 1 clearly shows the following. In the glass substrate of Example 1-9, it had a toroidal ring strength ratio of 1.5 or more which improved the strength 50% or more compared with the case where it was not chemically strengthened. The glass substrate had a flatness of 3 µm or less, which was satisfactory for use as an information recording medium.

On the other hand, in the glass substrate of Comparative Example 1 in which the alkali metal oxide content was large, the ion exchange reaction proceeded excessively in the chemical strengthening treatment, and the thickness of the reinforcing layer reached 120 μm, and the reinforcing layer of 70 μm remained on the recording surface even after the polishing treatment. For this reason, alkali elution amount increased to 623 ppb, and also the flatness became very high as 33 micrometers, and it became a glass substrate unsuitable for use in the information recording medium. In the glass substrate of Comparative Example 2, Al ₂ O ₃ / B ₂ O ₃ was 1.3, and the ion exchange reaction did not proceed stably in the chemical strengthening treatment, and no reinforcing layer was formed. Because of this, the glass substrate did not have increased strength. In addition, the glass substrate had a fragile structure and had a high Si elution rate of 709 ppb. In the glass substrate of the comparative example 3, since the total amount of alkali metal oxide was small at 4.0%, the strengthening layer was not formed in the chemical strengthening process. Moreover, the glass substrate had a Vickers hardness as high as 655, the workability was lowered, and the fracture toughness was as low as O.78, and the strength was low. Moreover, Si elution amount S was 563 ppb high. Although the glass substrate of the comparative example 4 had the same glass composition as the glass substrate of Example 5, 5 micrometers of reinforcement layers remain | survived on the recording surface with the amount of polishing by a grinding | polishing process being set to 20 micrometers (10 micrometers on one side) on both upper and lower sides. Such glass substrates were as high as 15 µm even after polishing, and thus were unsuitable for use for information recording media.

Next, the components of the chemical strengthening solution and the temperature and time of the chemical strengthening treatment were changed, and the thickness of the strengthening layer formed on the glass substrate was measured. The glass composition used the thing of Example 1 here. Then, it grind | polished to the predetermined thickness and measured the ring strength ratio and flatness of each glass substrate. The results are shown in Table 2.

TABLE 2

According to Table 2, it turns out that the thickness of the reinforcement layer formed in a glass substrate can be controlled by changing the component ratio, processing temperature, and processing time of a nitrate. Further, by removing the reinforcing layer formed on the recording surface and leaving the reinforcing layer only on the outer and inner circumferential surfaces of the glass substrate, the ring bending strength can be increased by 1.5 to 2.3 times, and the smoothness of the recording surface is 3 μm or less. Can be reduced.

Claims (7)

delete Glass substrate for chemically strengthened information recording media, Although a reinforcing layer by chemical strengthening exists on the outer circumferential surface and the inner circumferential surface, it does not substantially exist on the surface on which the information recording layer is formed, The glass component in the surface on which the information recording layer is formed is in weight%, SiO ₂ : 40-75%; Al ₂ 0 ₃ : 3-20%; B ₂ 0 ₃ : 0-8% (including 0); Total amount of at least one alkali metal oxide selected from the group consisting of Li ₂ O, Na ₂ O and K ₂ O: 5-15% ;, SiO ₂ + Al ₂ O ₃ + B ₂ 0 ₃ : 60-90%; Total amount of R'O (R '= Mg, Ca, Sr, Ba, Zn): 0-20% (including 0); TiO ₂ + ZrO ₂ + Ln _x 0 _y : 0-15% (Including 0, where Ln _x O _y is a group consisting of lanthanoid metal oxide and Y ₂ O ₃ , Nb ₂ 0 ₅ , Ta ₂ 0 ₅ Means at least one compound selected from A glass substrate for an information recording medium satisfying 1.5 <Al ₂ 0 ₃ / B ₂ 0 ₃ or B ₂ 0 ₃ = 0%. The glass substrate for an information recording medium according to claim 2, comprising 0.5% or more of K ₂ O by weight. The glass substrate for an information recording medium according to claim ₂ or _3, which contains 1.0% or more of B ₂ O ₃ in weight percent. 4. A glass substrate according to claim 2 or 3, comprising 0.5% -13% of TiO ₂ + ZrO ₂ + Ln _x O _y in total by weight. The inelastic modulus (E / ρ) of 30 or more, Vickers hardness Hv of 450-650, alkali elution amount A of 350 ppb or less per 2.5 inch disk, Si elution amount S of 50Oppb or less per 2.5 inch disk. And a fracture toughness Kc of not ^less than 0.8 MPa / m ^1/2 . An information recording medium according to claim 2 or 3, wherein an information recording layer is formed on the glass substrate.

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